Sandwich plate stepped risers

ABSTRACT

A two-tired seating riser for a sports stadium comprises upper and lower metal plates bonded together by a solid elastomer core. The elastomer core has different thicknesses in the treads and rises. The lower tread has a lip portion in which the metal plates are flared to facilitate alignment with the riser below.

[0001] The present invention relates to stepped risers, particularlyseating risers for sports stadia and other entertainment venues.

[0002] To increase the revenue from sporting and other events, it isdesirable to maximize the number of spectators that can be accommodatedin a sports stadium or other venue. To do this it is necessary toprovide additional tiers of seats, often resulting in structures inwhich a significant portion of the upper bowl seating cantilevers overother parts of the structure. Accordingly, the weight of riserssupporting such seating should be minimized to reduce the size and costof the supporting structure. To reduce transient and resonant vibrationsassociated with sporting and entertainment events the risers must bestiff, have sufficient mass, or be constructed with materials havinggood damping characteristics.

[0003] Existing designs of seating risers are made of prestressed orprecast concrete or steel. Known riser sections are generallyconstructed from concrete as it allows for long clear spans betweenrakers (typically 12,200 mm) with reasonable vibration control sinceconcrete has a damping coefficient of 0.2, good fire resistance andrelatively low maintenance cost. The major disadvantage of concreteconstruction is that the riser section is heavy, e.g. about 10T for atwo tier riser, with self weight (deadload) equal to the designsuperimposed live load due to use and occupancy. It is thereforenecessary to provide heavier, stronger, stiffer and more costlysuperstructure and foundations to support the riser sections, especiallyfor large cantilever seating sections.

[0004] To minimise self weight, and hence reduce the cost of thesuperstructure and foundations, the riser sections may be constructedwith folded steel plates that are supported by intermediate rakers and asecondary steel framework. Typically the maximum span for this type ofconstruction is approximately 6100 mm and the self weight about 40% ofan equivalent concrete structure. However, steel risers are moresusceptible to sound and vibration problems, having a dampingcoefficient of 0.1, and have additional costs associated with thefabrication and erection of the intermediate rakers and secondary steelframework.

[0005] Accordingly it is an aim of the present invention to provide animproved seating riser, for example that is lighter, simpler inconstruction and/or better damped.

[0006] According to the present invention, there is provided a steppedriser comprising a sandwich structure having upper and lower metalplates and an intermediate layer of a plastics or polymer materialbonded to said metal plates so as to transfer shear forces therebetween.

[0007] The sandwich structure plates used in forming the stepped riserhave increased stiffness as compared to steel plates of comparablethickness and avoid or reduce the need to provide stiffening elements.This results in a considerably simpler structure with fewer welds ornone leading to both simplified manufacture and a reduction in the areavulnerable to fatigue or corrosion. Further details of sandwich platestructures suitable for use in the present invention can be found inU.S. Pat. No. 5,778,813 and British Patent Application GB-A-2 337 022.The intermediate layer may also be a composite core as described inBritish Patent Application No. 9926333.7.

[0008] The outer upper and lower metal plates preferably have athickness in the range of from 2 to 10 mm and the intermediate layer inthickness in the range of from 10 to 100 mm. To provide space forseating, the run (depth) of the risers is preferably in the range offrom 600 to 1200 mm. The slope of the risers is preferably in range offrom 20° to 45°. The outer metal plates are preferably parallel but neednot be.

[0009] The present invention provides a riser having one or more tiers(steps), typically two, and offers unique advantages over traditionaltypes of construction by providing long clear spans, e.g. of 6 to 20 min length, that are comparable to prestressed or precast concrete whileweighing approximately 70% less and by providing a less complexstructure which does not need the secondary steel work associated withall-steel risers of the same span. The plastics or polymer (e.g.polyurethane elastomer) core acts as a natural damper, reducingvibrations (damping coefficient for risers according to the inventioncan be between 0.4 and 0.5) and provides excellent sound insulation;improving both comfort and safety. In addition, the constructionprovided by the present invention allows for the use of dissimilarmetals without welding. Therefore corrosion-resistant stainless steel,that reduces maintenance, improves life span and maintains its visualattractiveness, can be used for the wearing exposed surface inconjunction with less expensive structural steel for the undersidesurface, that can be welded or bolted through T-stub sections which arebolted to raker beams. The structured steel may be galvanised or coatedwith epoxy or zinc rich paint to provide the appropriate corrosionprotection.

[0010] The riser sections can be fabricated under controlled conditionsto provide a quality structural section with good dimensional accuracy.The connections for railings, seating and longitudinal joint seals canbe similar to those for prestressed or precast concrete. Drip lips andinterlocking longitudinal seams can be included to facilitate waterrunoff and erection, and to limit horizontal deflections of the risers.

[0011] Integral guides, interlocking and drip extended riser plates aswell as bolted connections in embodiments of the invention simplifyplacement and installation of the riser. Two-tier risers are alignedwith the lower section via guide plates and bolted to the raker beams.Additional bolts provided along the guide edge, e.g. at every 1000 mm,prevent de-bonding if one of the two plates is accidentally pulled openduring transportation or installation.

[0012] Alternatively, the sandwich plate risers may be welded closed tocompletely encase the plastic core. This simplifies fabrication ofshaped sections, e.g. wedge shaped sections at the ends of a bowl, byeliminating the need for more complex adjustable jigs to form anenclosure for casting of the plastic core. In addition, this type ofsection, without any exposed plastic along the edges, has excellent fireresistance and may be used in parts of the stadium that must be designedto resist fires.

[0013] A riser according to the present invention can be designed tomeet relevant serviceability criteria and construction constraintsrelated to vibration and deflection control, and plate handling. Thestrength and stiffness of the treads and risers can be tailored toimprove performance while minimizing cost and weight by specifying twodifferent core thicknesses. The resulting structure is light, stiff and,with the core's inherent dampening characteristics, provides improvedstructural and vibration response performance over risers built withstiffened steel plates and rolled sections (secondary steel work) orthose built with prestressed concrete.

[0014] The present invention will be described further below withreference to the following description of an exemplary embodiment andthe accompanying schematic drawings, in which:

[0015]FIG. 1 is a plan view of a sports stadium in which the seatingriser of the present invention may be used;

[0016]FIG. 2 is a cross-sectional view of section of the stadium of FIG.1 in which seating risers according to the present invention are used;

[0017]FIG. 3 is perspective view of a seating riser according to a firstembodiment of the present invention that is constructed without welding;

[0018]FIG. 4 is an end view of a welded seating riser according to asecond embodiment of the present invention;

[0019]FIG. 5 is a cross-section of part of the seating riser of FIG. 3illustrating the connection to the upper raker and to an adjoiningriser;

[0020]FIG. 6 is a view, similar to FIG. 5 of the seating riser of FIG.4;

[0021]FIG. 7 is an enlarged perspective view of part of the seatingriser of FIG. 3 showing how the riser is fixed to a raker bracket;

[0022]FIGS. 8 and 9 are perspective views of alternative raker brackets;

[0023]FIG. 10 is a top view of the mounting bracket of FIG. 8 welded toa seating riser according to the invention;

[0024]FIG. 11 is a perspective view showing an arrangement for mountinga railing to a seating riser of the present invention;

[0025]FIG. 12 is a perspective view showing an alternative arrangementfor mounting a railing to a seating riser of the present invention;

[0026]FIG. 13 is a perspective view showing an arrangement for mountinga seat bracket to a seating riser of the present invention;

[0027]FIG. 14 is a cross-sectional view showing a sealing arrangementbetween two seating risers according to the present invention;

[0028]FIG. 15 is a cross-sectional view showing an alternative sealingarrangement between two seating risers according to the presentinvention;

[0029] FIGS. 16 to 18 show in plan alternative shapes of riser; and

[0030]FIG. 19 is a cross-section of an alternative form of riser,according to the invention.

[0031] In the various drawings, like parts are denoted by like referencenumerals.

[0032]FIG. 1 shows a sports stadium 1 having on one side an elevatedstand (upper bowl) 2 which includes raked seating sections 3. Theseseating sections are approximately rectangular at midfield and flareoutwards, at the edges of the stand so as to be tapezoidal(wedge-shaped) in plan. The seating sections 3 typically have a width ofabout 36 feet (about 11 m) at the lower end and about 40 feet (about 12½ m) at the upper or outer edge. A cross-section through such a seatingsection is shown in FIG. 2. As can there be seen, the upper bowl of thestand consists of a series of seating risers 4 mounted on raker beams 5which cantilever over other parts of the stadium. Seating risers mayalso be placed on several levels to maximise the number of seats withoptimum viewing position.

[0033] A two-tier riser 4 is shown in perspective in FIG. 3 andcomprises upper and lower treads 41, 42 joined by first rise 43. Secondrise 44 projects upwardly from the back edge of first tread 41 and a lip45 projects downwardly from the front edge of tread 42.

[0034] The two-tier riser can be formed by two folded plates 10, 11, forexample of thickness 4 mm, and a plastic core 12, e.g. of structuralpolyurethane elastomer, with a thickness of 40 mm, for example, in thetreads and 20 mm, for example, in the rise as illustrated in FIG. 4. An11 m riser weighs approximately 3T or 30 pounds per square foot (about145 kgm⁻²) of projected horizontal area. The steel sections can be madewith a single rolled plate that requires limited cutting to size theplate prior to folding or roll forming. The folded plates are placedinto a steel mould (jig) with appropriate spacers (e.g. shear studs orplastic (elastomer) spacers) and side mould sections. The mould isclosed and the polyurethane elastomer core injected into the closedcavity, e.g. via one or more Puromat PU150 high-pressure meteringmachines in approximately 200 to 400 seconds. The gel and setting ischosen to commence after injection is complete. The section can beremoved from the mould within an hour. The use of a mould (jig) ensuresthat relatively thin folded steel plates are properly placed andsupported so that dimensional accuracy is achieved. Drilled bolt holes,final sizing by cold cutting (wedge shaped sections only, if required)and epoxy coat application to the structural steel plate completes theriser section. Shop fabrication and finishing ensuresa high qualitystructural product. Sections can be prefabricated and stored offsiteuntil required. Doubler plates can be welded to the structural plateprior to injection of the core material to decrease localized bearingstresses at the bolted connections which join the riser sections to theraker beams.

[0035] The riser sections include appropriate detailing (built in guideswith flared edges for alignment, drip lips, caulking joints, liftingattachments) to facilitate lifting, simplify placement and installation.The riser sections, being stiff and relatively light compared toconcrete sections, are easily lifted and bolted into place. Risersections according to the invention may be erected more quickly thanconcrete risers as they are tougher and not susceptible to chipping andcracking if the section is mishandled during placement. Longitudinaljoint sealant is applied and prefabricated stainless steel stairsections are bolted into place. Seating and handrail installation can becompleted by methods similar to those used for prestressed concreterisers, e.g. drilling and bolting using for example Hilti (TM) expansionor epoxy bolts or anchors. Speciality attachments and drainage detailscan be provided as desired.

[0036]FIG. 4 is an end view of an alternative construction in which theriser 4′ is welded to completely encase the plastic core. The upperplate 10′ and lower plate 11′ are folded to close the long edges, toprovide simple weld details and to make matching male and female edges61, 62 suitable for bolting adjoining riser sections as illustrated inFIG. 6. End plates 100 are cut to shape, fitted and welded at both endsto close the section.

[0037]FIGS. 5 and 6 show details of the connection between a first riser4-1 and second riser 4-2 or 4′-2 as well as the mounting of the firstriser 4-1 or 4′-1 to the raker beam 5. The second rise 44 of first riser4-1, 4′-1 engages in the lip section 45 of the upper riser 4-2, 4′-2.The lip section 45 has flared edges 47, acting as drip lips, and, fornon-welded constructions, bolts 46 holding the inner and outer plates10, 11 and core 12 together to prevent delamination in the event ofrough handling in transport or misalignment on installation. In thewelded embodiment, bolts 46′ join the male end 61 of riser 4′-1 tofemale end 62 of riser 4′-2. To mount each riser to the raker beam 5,T-shaped brackets 6 are provided. These are bolted to the rises 44, 43of the seat risers 4 and also to the raker beams 5 by bolts 62, 61.

[0038]FIGS. 5 and 6 show the positioning of a T-shaped bracket 6 at theedge of a seat riser so that two longitudinally adjacent risers arebolted to a single bracket 6. The brackets 6 are bolted, as shown inFIG. 7, to the raker beams 5 prior to the placement of the risersections and act as alignment guides to assist location of theprefabricated risers on installation.

[0039] An alternative bracket 6′, shown in FIG. 8, has a flat front-face63 prepared for welding to the back of the rises 43, 44; this is shownin FIG. 10. Another alternative bolted bracket 6″ shown in FIG. 9contains a seating angle 101 to facilitate erection.

[0040]FIGS. 11 and 12 show alternative arrangements for attachment ofrailing posts 7, 7′. As shown in FIG. 4, a railing post 7 can be boltedor anchored via bracket 71 to rise 44 of first riser 4-1, near itsjunction with horizontally and vertically adjacent risers 4-2, 4-3 and4-4. In FIG. 12, railing post 7′ is welded to an L-shaped bracket 73 sothat railing post 7′ extends upwardly from the lower tread 42 of riser4-2. The bracket 73 extends over the edge of riser 4-2 and is bentaround lip section 45 to be bolted or anchored to upper rise 44 of riser4-1, in addition to a bolt or anchor connection to lower tread 42 ofriser 4-2.

[0041]FIG. 13 shows an arrangement for attaching a seat bracket 8; thiscan be bolted or anchored to the upper rise 44 of riser 4-1.

[0042] Two possible longitudinal joint sealant details 50, 50′ toprevent water penetration between the ends of two riser sections areillustrated in FIGS. 14 and 15. The first FIG. 14) utilizes caulking 50(similar to prestressed concrete risers) and the second (FIG. 12)utilizes a flexible membrane 51 or corrugated flexible stainless steelstrip that can be bonded to the outer plate 10 of each riser 4 with atwo sided structural tape 52 that bonds the strip to the 4 mm stainlesssteel plate as though it were welded. An additional protective stainlesssteel sheet 53 can be provided on top of membrane 51 where it is bondedto the riser. The caulking or flexible strip allows expansion orcontraction across the joint due to changes in the length of the risersection caused by seasonal temperature changes and can easily beinstalled once the tier sections are bolted into place.

[0043] The two-tier riser of the present invention can withstandcritical load combinations comprising one or more of the following: selfweight, seating dead load of 0.14 kPa (3 psf), use and occupancy liveload of 4.8 kPa uniformly distributed on the horizontally projectedsurfaces (treads, 100 psf) or applied through the seat brackets, windload of 1.92 kPa (suction or pressure), snow load of 1.2 kPa and theappropriate railing loads with the appropriate load factors. All boltedand welded connections can conform to CAN/CSA S16.1-94 Limit StatesDesign of Steel Structures. The maximum frequency of vibration for thefirst three fundamental modes can be limited to 1 Hz. In addition, eachtier can be designed to accommodate changes in length due to atemperature fluctuation of ±40° C., (72° F.). This is achieved byoversized holes for the bolted connections at either end to accommodatechanges in length due to temperature changes.

[0044] In variations of the present embodiment, the folded plates areplaced in a mould (jig) with elastomer spacers and side mould sections.The mould can be constructed to accommodate varying positions of one orboth side mould sections to allow variable widths or wedged shapesections to be made. The mould can also provide fixed adjustments toaccommodate variable riser heights and tread lengths. Drainage can beeasily accomodated by cambering or sloped treads. Slip-resistant wearingsurfaces can be incorporated using profiled plates, e.g. of checkerboard pattern, for upper plate 10.

[0045] Wedge shape sections (for use where mitered edges betweenadjacent rakers are desired, e.g. in flaring seating sections) may beeither made to the correct plan dimensions or made square to the longestplan dimension and cut to the correct wedge shape with a fine-toothband-saw.

[0046] FIGS. 16 to 18 show in plan alternative shapes of riser. Thebasic form of riser 110, shown in FIG. 16, is rectangular in plan andhas a length L in the range of from 6 to 20 m. For curved or polygonalsections of stand a riser 111 of trapezoidal plan as shown in FIG. 17may be used. In such a riser, the maximum length L may be in the rangeof 6 to 20 m but the minimum length 1 somewhat less. For corner sectionsa riser 112 of triangular plan as shown in FIG. 18 may be used. Themaximum length L of such a riser may be as small as required. Morecomplex shapes for specific purposes may also be provided.

[0047]FIG. 19 shows in cross-section an alternative form of riser 113.This riser 113 has an upstanding wall section 114 at the outer edge ofthe lower tread 42 so that the wall section 114, tread 42 and rise 43form a “bathtub” section. The wall section 114 forms a perimeter fencewhen the section is used at the bottom of tiers or sealing sections. Thetop of the wall section 114 may be angled or curved to preventspectators resting objects, such as drinks, on it.

[0048] Materials

[0049] The upper and lower metal plates 10, 11, and other metal parts ofthe riser section described above, are preferably made of structuralsteel, as mentioned above, though these may also be made with aluminium,stainless steel, galvanised steel or other structural alloys inapplications where lightness, corrosion resistance or other specificproperties are essential. The metal should preferably have a minimumyield strength of 240 MPa and an elongation of at least 10%.

[0050] The intermediate layer (structural plastic core) should have amodulus of elasticity, E, of at least 250 MPa, preferably 275 MPa, atthe maximum expected temperature in the environment in which the memberis to be used. In civil applications this may be as high as 100° C.

[0051] The ductility of the core material (plastics or polymer) at thelowest operating temperature must be greater than that of the metallayers, which is about 20%. A preferred value for the ductility of thecore material at lowest operating temperature is 50%. The thermalcoefficient of the core material must also be sufficiently close to thatof the steel so that temperature variation across the expected operatingrange, and during welding, does not cause delamination. The extent bywhich the thermal coefficients of the two materials can differ willdepend in part on the elasticity of the core material but it is believedthat the thermal expansion coefficient of the core material may be about10 times that of the metal layers. The coefficient of thermal expansionmay be controlled by the addition of fillers.

[0052] The bond strength between the core and metal layers must be atleast 0.5, preferably 6, MPa over the entire operating range. This ispreferably achieved by the inherent adhesiveness of the core material tometal but additional bond agents may be provided.

[0053] The core material is preferably a polyurethane elastomer and mayessentially comprise a polyol (e.g. polyester or polyether) togetherwith an isocyanate or a di-isocyanate, a chain extender and a filler.The filler is provided, as necessary, to reduce the thermal coefficientof the intermediate layer, reduce its cost and otherwise control thephysical properties of the elastomer. Further additives, e.g. to altermechanical properties or other characteristics (e.g. adhesion and wateror oil resistance), and fire retardants may also be included.

[0054] Whilst an embodiment of the invention has been described above,it should be appreciated that this is illustrative and not intended tobe limitative of the scope of the invention, as defined in the appendedclaims. In particular, the dimensions given are intended as guides andnot to be prescriptive. Also, the present invention has been exemplifiedby description of a seating riser but it will be appreciated that thepresent invention is applicable to other forms of stepped structure.

1. A stepped riser comprising a sandwich structure having upper andlower metal plates and an intermediate layer of a plastics or polymermaterial bonded to said metal plates so as to transfer shear forcestherebetween.
 2. A stepped riser according to claim 1 wherein said riseris a seating riser.
 3. A stepped riser according to claim 2 furthercomprising mounting details for at least one seat and/or railings.
 4. Astepped riser according to any one of claims 1 to 3 wherein said riserhas a maximum length of from 6 to 20 m.
 5. A stepped riser according toany one of the preceding claims wherein said stepped riser has a run offrom 600 to 1200 mm.
 6. A stepped riser according to any one of thepreceding claims wherein said upper and lower metal plates are formed byfolding or roll-forming respective flat plates.
 7. A stepped riseraccording to any one of the preceding claims wherein said intermediatelayer is thicker in treads of said stepped riser than in rises.
 8. Astepped riser according to any one of the preceding claims wherein saidstepped riser comprises one or more generally horizontal treads and oneor more generally vertical rises.
 9. A stepped riser according to claim8 wherein one of said rises joins the front edge of an upper one of saidtreads to the rear edge of a lower one of said treads and a said secondrise extends upwardly from the rear edge of said upper tread, the frontedge of said lower tread having a downwardly projection lip portion. 10.A stepped riser according to claim 9 wherein said upper and lower platesare flared in said lip portion to receive an upper edge of an upper riseof a like stepped riser.
 11. A stepped riser according to any one of thepreceding claims wherein said upper plate is made of a different metalor alloy than said lower plate.
 12. A stepped riser according to claim11 wherein said upper plate is more corrosion resistant than said lowerplate.
 13. A stepped riser according to any one of the preceding claimswherein said upper plate is thinner than said lower plate.
 14. A steppedriser according to any one of the preceding claims wherein said upperplate is provided with a corrosion prevention treatment such aszinc-rich paint, epoxy paint or galvanising.
 15. A stepped riseraccording to any one of the preceding claims wherein said upper platehas a thickness in the range of from 2 to 10 mm, said lower plate has athickness in the range of from 2 to 10 mm and said intermediate layerhas a thickness in the range of from 10 to 100 mm.
 16. A stepped riseraccording to any one of the preceding claims wherein said intermediatelayer is formed of a plastics material, preferably a compact elastomer.17. A stepped riser according to any one of claims 1 to 16 wherein saidintermediate layer comprises a form and said plastics or polymermaterial, which occupies the space between said upper and lower metalplates not occupied by said form.
 18. A stepped riser according to claim17 wherein said form comprises foam and said plastics or polymermaterial is elastomer.
 19. A spectator stand having at least one steppedriser according to any one of the preceding claims.